Insulated metal substrates are being used for the mounting and interconnection of light emitting diodes (LEDs) in applications such as display back lighting, automotive lighting and general commercial and consumer lighting uses. The substrates currently being used are generally rigid and are not able to be deformed and bent without degradation or damage to their mechanical, electrical and thermal properties. It is desirable to be able to form or bend such substrate materials to make angles, curves or bends, while maintaining mechanical and thermal integrity and without causing degradation of the substrate or of its electrical properties.
Multi-functional electronic substrate materials of various kinds are known in the art. Some of the layers of these substrates can be made of various polymer materials such as polyimide (hereinafter referred to as “PI”). In general, these are rigid structures with little flexibility, unless the structure is grooved.
US 2007/0076381 A1, for example, describes a flexible heat spreader circuit board with a heat sink. The flexibility of its circuit board results from a pattern of grooves that make an upper surface and a lower surface flexible when the substrate is bent.
Aluminum substrates are known for use in visible LED Circuits. Canadian Electronics Magazine e-magazine, for example as shown in an article titled “Aluminum Substrates Make light work of visible LED Circuits” by Tom Morris, dated Sep. 18, 2007. Economical solderable polymer thick film conductors can be screen printed directly onto such substrates, without degradation. The article mentions that aluminum alloy substrates can be extruded, die cast and made in special shapes. The thermally conductive aluminum alloy material enables design engineers to mount high power LED components directly to it. However, no mention is made of any flexibility of such alloy substrates.
In an article titled “Poor fixtures threaten to jeopardize the illumination potential of LEDs” by Richard Stevenson, Compound Semiconductor, June 2007, the author points out that the low efficiency of many fixtures in the industry results from lack of skills relating to working on the design aspects of these fixtures, by the workforce of many companies, who work with the electrical systems used in powering LEDs. These techniques are needed for thermal management and optical design.
As applications expand requiring more complex mechanical configurations and circuitry becomes thinner and more complicated, it is desirable for the substrates to be shapeable without any resulting degradation of the substrate surface characteristics or without interfering with their thermal or electrical properties. It is also desirable for chosen substrates to be cost effective, be easy to handle and be able to be used in fixtures allowing the best use of the light from an LED. The laminate described in the present patent application is useful in such fixtures as it can be shaped for improved optical properties without any degradation of its electrical properties and with its thermal properties maintained. The ability to bend a laminated structure without degrading the electrical circuitry allows the configuring of LED's in a “3D” format. Such structures are not limited to a planar format. Having this bendable ability provides the device designer with more options to tailor and optimize the device design. Overcoming the limitations in LED mounting and LED structure and fixtures imposed by rigid substrate materials and interconnection materials allows the designer to customize and optimize the mechanical features found in Solid State lighting components.
The present flexible structure is expected to increase overall optical electrical efficiency from 30% to 40% of the range currently seen in LED structures and to optimize the configuration manually by allowing the bending at the most efficient configuration to concentrate and disperse LED light.